DETROIT — General Motors, once the colossus of American capitalism, will become a leaner, government-owned company if the Obama administration goes along with the automaker's plan to slash jobs, close plants and eliminate the legendary Pontiac brand.

As GM laid out the proposal yesterday, new agreements fell into place between Chrysler and its unions in the United States and Canada, making it apparent that the future of both companies now rests with their creditors.

General Motors CEO Fritz Henderson said the company would offer the Treasury Department more than 50 percent of its stock to absolve GM of $10 billion in government loans.

The automaker also proposed that the United Auto Workers take GM stock for at least half the $20 billion the company owes to a union-run trust that will assume retiree healthcare expenses starting next year.

Combined, the union and government would own 89 percent of the century-old automaker, which has been bleeding red ink and is saddled with more than $62 billion in debt.

"It is unprecedented, but it signifies the importance of the automobile industry," said David Lewis, a retired professor at the University of Michigan who taught business history for 43 years.

Although the government has loaned money to corporations in the past, including to Chrysler in the 1970s, Lewis could not recall a time when it had taken a majority stake in a company.

White House press secretary Robert Gibbs said the administration does not want to own GM or any other auto company.

"This administration has no desire to run an auto company on a day-to-day basis," Gibbs said. "We strongly back an auto industry we believe can, and should, be self-reliant of government funding."

But GM's plan depends on persuading unsecured bondholders who have loaned GM $27 billion to forgive that debt in exchange for a 10 percent stake in the company.

Current GM shareholders would own only about 1 percent.

GM's announcement sent its shares up 21 percent to $2.04 yesterday, meaning bondholders would get about 46 cents on the dollar.

General Motors is surviving on $15.4 billion in government loans, and said yesterday in a filing with the U.S. Securities and Exchange Commission that it envisions getting an additional $11.6 billion.